Method of impressing plastics



Patented Dec. 1942 I Ma'ron or MraassNG rLAs'rcs Arthur M. Wickwire, Jr., Mountain Lakes, and

John Muller, Waldwick, N. J., assignors to Peerless Roll Leaf Co., Inc., Union City, N. J., a corporation of New York Application February 11, 1939, Serial No. 255,905

3 Claims.

The invention relates to the method of impressing plastic material with stamping media.

stamping media, including the heat releasable type, have been employed generally with success ing permanent retention of the outer sizing of the W Vstamping medium. I

Illustrations of suitable plastic material are: phenol-formaldehyde compounds, phenol-fur- I (Ci. 41-37) vinyl chloride-acetate resins, methyl-methacrylate resins, styrene resins, shellac compounds, synthetic rubber compounds, celiulose compounds such as (a) ethyl cellulose, (b) cellulose acetate.

under commercial conditions for impressing and 5 (c) cellulose nitrate, casine compounds, 'synthetic ornamenting materials of various character, but alkyds, and modified oils, and the like; possessing the attribute of yielding under pres- Examination of the derived stamped product sure of the stamping press. Such conventional revealsthat the stamped deposit makes a subpractice has been carried out under the condition stantially continuous contact withthe facial porthat the material stamped is at atmospheric temtion of the plastic, the local face'portions of the peratures. With heat releasable stamping purmaterial immediately adjacent the stamped desuant to such conventional practice, the die is posit being ridged about' the stamped deposit, heated, usually by means of a controlled electrithus dening a sight and surrounding the stampcal resistance heating element, it being undering with what might be described as a raised stood that the stamping medium is interposed frame.

between the face of the die and the material to The above listed plastics, in current use, are be stamped. characterized as molded at temperatures from It has long been desired to stamp plastics, buti approximately 225" IF. upwardly, under compresall efiorts to obtain commercially satisfactory imsion molding pressures of from 1000 pounds per pressions within commercially acceptable propor- W square inch and upwar'lly, and, possessing the tion of spoilage following conventional practice, attributeV of having substantially no tendency have failed. This has been due to many causes, to cold flow, i. e., at atmospheric temperatures. a primary cause being that the facial area of a Further features and objects of the invention moided plastic due to inherent physical characwill be more fully understood from the following teristics and imperfections unavoidable in the detail description and the accompanying drawmolding operation, is not uniplanar, but on the ing, in whichcontrary is formed of irregular undulations of Fig. 1 is a side elevation, largely diagrammatic. hills and "dales." The stamping medium, pur- ,illustrating steps of a preferred procedure in suant to conventional practice, if attached'at all, carrying out the invention, with respect to a is attached solely to the apices of the hills," and series of plastic articles; wholly unattached at the dales," and subject to Fig. 2 is a 'central vertical section, diagramready dislodgement and otherwise commercially matically illustrating a die of a stamping press.' unacceptable. If'it is sought to apply pressurea' length of stamping medium and a section of a greater than that of usual practice, in the effort plastic article, the faces of which are exaggerated to lodge the stamping medium in contact in undulating facial characteristics; throughout with the surfaces of the hills and Fig. 3 is a view similar to that of Fig. 2, showing "dales. fracture or breakage of the plastic enthe die and therewith engaged stamping medium sues, by reason of its brittleness. in pressure-engagement with a portion of an up- We have discovered that when a molded mass per face ofaplastic article; and v oi' plastic material of the nature hereinbelow set 40 Fig. 4 is a vertical section of ,a plastic article forth. is preheated to a. minimum predetermined. succeeding the stage of stamping, pursuant to temperature, the material of the face portion of the hereinabove indicated procedure.- the plastic desired to be stamped adapts itself to Referring to the drawing, i. indicates an arthe contours of the design transmitting elements` ticle of plastic material, of the nature hereinofthe die by local displacement of the face. maabove set forth. l'l indicates'a suitable preheater terial, and commercially satisfactory stamping is referred to more fully hereinafter. l2 represents obtained attended lby minimum spoilage. Fura suitable stamping press, the platen of which is ther, particularly 'with heat releasable stamping indicated at li. I 4

medium, the face portion of the material of the specifically, the stamping press is preferably plastic attains physico-chemical attributes -eflectof the type set forth and claimed in the U. S.

Patent No..2,122,669, dated Julyl, 1938, granted to Arthur M. Wickwire, Jr. An advantage attained by 'the stated Wijckwire stamping press of particular value in carrying out the instant ini fural compounds, urea-formaldehyde compound's, V vention resides inthe self-adjusting mounting of the platen, i. e., upon mutually' related springtensioned toggles, indiated at ll whereby the platen accommodates itself to varying mean vertical dimensions of the article to be stamped, to

present the mean plane of the face of the article to be stamped substantially at right angles to the face of the die' li carried by the movable plunger II, to which the die holder l'I is secured.

When practicing the invention under corn-l mercial conditions, a suitable conveyor indicated at ls may be provided, for conveying the variant plastic articles ll, ll, etc. in seriatum through the preheater ll to a position readily accessible to the operator of the stamping press ll.

A preheated article of any given plastic, designated llla, in Figs. '1, 2, 3, and 4, upon having its temperature raised to its proper predetermined temperature, is s hown in Fig. 1, in position upon the platen li of the stamping press. The stamping medium indicated at li is suitably fed to the face lia of the die li.

Preferably, the stamping medium l! is of the heat releasable type. that is to say, embodying an inert carrier such as paper, or cellulose i'ilm of which the product known under the trademark Cellophane is a prominent illustration. or glassine paper or the like, upon one face of which is a layer of oleaginous heat releasable material, usually embodying beeswax, rosin or like resinous mixture; up'on such oleaginous layer is applied gold illm or leaf such as beaten gold, electrolytic goldl or the like, or imitation leaf" such as bronze powder for imitation gold," aluminum powder for imitation silver, `ietc. The stamping medium has an outermost layer of sizing, which may be s hellac or the'like, which may or may not have a pigment therein. i

a,sos,ase

ing press and within which range of temperature lthe mass of the plastic article loses the characteristic of brittleness under the 'stamping pressure and also maintains in substantial permanency its physical dimensional characteristics. Fortuitously, the plastic compositions in current general use, enumerated in the hereinabove appearing list, attain the above referred to facial displacement and mass non-brittleness and permanency of dimension characteristics within the approximatel range. from 130 F. upwardly, the upper limit being usually less than 250 F. The results of our discovery indicate, by reason of the local cold flow characteristic imparted to the surface portions of the plastic article, preheated as above set cut, that thereby the inner mass of the plastic article, having a definitely lower temperature, is protected from fracture.

'Predicated upon the results of our discovery, the temperature to which the die is heated, i. e., by its individual heating element, may, and preferably, approximates closely the minimum temperature of the stated range of preheated-temperature of the plastic.

specifically, plastic articles of phenol-formaldehyde compounds of the type sold under the trade-mark f'Bakelite" are commercially satisfactorily stampedl pursuantto our invention, as aforesaid, when preheated to a temperature range between 140' F. and 150 F.

Under optimum temperature conditions of the preheated plastic article and of the heated dle, as based upon the results of our discoveries, the pressure of the impression, i. e., exerted by the stamping press, may be somewhat less than that pursuant to conventional practice in the use of the particular stamping medium employed.-

The assembly of a die II, the heat releasable 1 stamping medium ll 'and the preheated plastic article ila, at al stage`immediately prior to the stamping operation, is diagrammatically illustrated in Fig. 2. As appears from Fig. 2, the upper face llib of a molded plastic article is nonplanar, the undulations being somewhat exaggerated, for the purpose of clarity' of illustration. In the employment of a heat-releasable stamping medium, the die holderl l'l. is heated by its heating element, not shown, pursuant to `conventional practice employing a heated die assembly.

` Figure 3 iilustrates diagrammatically the stage of stamping, that is' to say, the stage whereat the heated die IS has brought the stamping medium l! into contact' with the undulated face lllb of the plastic article, and the impression face .of the die and the interposed stamping medlum into forceful impression contact with thev 6 during the stageof and continuing after the stage of the stamping operation, the elements li' constituting the sight of the impressed stamping and the ridges l0 d in similitude of framing about the impressed stamping elements li'.

Stated generally, the preheating of an article of any given, plastic lcomposition is carried to a range of temperature within which -th'e surface portions of its mass attains the characteristic of For the purpose of simplicity `and clarity of terminology, we have employed the term ther- -mo-stampable" plastic as denning any plastic comprised in the above appearing list and possessing the characteristics of being moldable at temperatures from approximately 225 F. up;- .wardly, under vcompression molding pressure of from 1000 pounds per vsquare inch and upwardly, possessing the attribute of substantially no tendency to cold flow, i. e., at atmospheric temperatures under conventional stamping pressure, and having the characteristic of brittleness at atmospherictemperatures.

whereas we have described our invention by reference to speciflc forms thereof, it will be understood that many changes and modifications may be made without departing from the spirit of the invention.

We claim:

1. The method of -stamping with metallic foil an article of thermo-stampable plastic which is brittle at atmospheric temperatures under pressure of stamping with a heated die, s aid methodv comprising heating such article to a temperature at which a facial portion of such article is locally displaceable under stamping pressure while the mass of the article maintains its dimensional 5 characteristics and is protected from tendency of brittleness under stamping pressure, providing a die bearing 'on its face the desired metallic conilgurated impression, providing a heat releasable metallic foil strip embodying a carrier strip bearing on its face a layer of heat releasable bonding medium -upon which is' applied metallic foil bearing on-its exterior face a bonding medium, heating the die face,, passing such heat releasable metallic foil strip in contact with the heated die local cold iiow under the pressure o f the stampface. and bringing the die and the thus inter-posed i metallic foil strip in pressure contact with the plastic article while the latter is in its stated heated status.

2. The method of stamping with metallic foil a molded article of thermo-stampable plastic which is brittle at atmospheric temperatures under pressure of stamping with a heated die and is moldable under compression of from 1000 pounds per square inch and upwardly under temperature of from 225'* F. upwardly, which comprises heating such article to a temperature at which the facial portion of such article is locally displaceable under stamping pressure while the mass of the article maintains its dimensional characteristics and is protected from tendency of brittleness under stamping pressure, providing a die bearing on its face the desired metallic configurated impression, providing a heat releasable metallic foil strip embodying a carrier strip bearing on its face'a layer of heat releasable bonding medium upon which is applied metallic foil bearing on its exterior face a bonding medium, heating the die face, passing such lheat releasable metallic foil stripl in contact with the heated die face, and

status, the stamping pressure being definitely less than the stated compression molding pressure of the plastic.

3. The method of'stamping with metallic foil a molded article of thermo-stamp'able plastic which is brittle'at atmospheric temperatures under pressure of stamping with a heated die and is moldable under compression of from 1000 pounds per square inch and upwardly under temperature of from 225 F. upwardly, which comprises heating such article to a temperature definitely less than its ;stated molding temperature and under a pressure definitely less than its stated molding pressure to render its facial portion locally displaceable i under stamping pressure while the mass of the article maintains its dimensional characteristics and is protected from tendency'of brittleness under stamping pressure, providing a die bearing on its face the desired metallic configurated impression, providing a heat releasable metallic foil strip embodying a carrier strip bear-` ingon its face a layer of heat releasable bonding medium uponwhich is applied metallic foil bearing'on its exterior face a bonding medium, heating the die' face, passing such heat releasable metallic foil trip in contact with the heated die face, and bringing the die and the thus interposed metallic foil strip in pressure contact with the plastic article' while the latter is in its stated heated status. I

- ARTHUR M. WICKMRE, Jn.

JOHN MUHIER. f: f i 

